Oxide coated articles with metal undercoating



United States Patent Ofi 3,006,782 Patented Oct. 31, 1961 ice Theinvention relates to oxide coated articles and provides an improvementtherein and in the art 'of making them. This application is a divisionof my copending application Serial No. 570,602, filed March 9, 1956.

A typical flow diagram for the process is as follows:

Article to be coated Metal undercoating applied as spray, electric arcsputteriug or electroplate, etc.

Spray on retractory oxide coating One object of the invention is toprovide flame resistant articles. Another object of the invention is toprovide metal articles coated with refractory material which isoxidation resistant and providing further protection against oxidationfor the underlying metal. Another object of the invention is to makecertain articles resistant to dampness and moisture. Another object isto provide superior refractory coatings on articles which coatings arestrongly adherent under diverse conditions of use. Another object is toprovide composite articles which are flame resistant and which can beeasily manufactured. Another object is to provide erosion resistantarticles which are also resistant to oxidation.

Another object of the invention is to provide a coating on steel partsfor use in aircraft engines and gas turbines giving them longer life.Another object is to provide a coating for combustion chambers andnozzles of rocket motors and the like to give them longer life. Anotherobject is to provide superior coverings tor rockets and aircraft.Another object is to provide a coating of refractory oxide on a metalpart without the use of the step of extreme roughening of the surfacebeing coated, by severe sandblasting or gritblast-in'g to obtain maximumadhesion. Another object is to provide a coating on metal articles withimproved thermal shock resistance.

Another object of the invention is to provide a superior class ofcoatings for such materials as plastics, carbon, and graphite. Anotherobject is to provide a refractory coating which is also substantiallyimpermeable for vari' ous materials such as those mentioned. Anotherobject of the invention is to provide bearing surfaces resistant tooxidation 'at high temperatures. Another object is to provide bearingsand bearing surfaces that are resistant to corrosive conditions. Anotherobject is to provide an adherent construction for multiple and forsandwich coatings. Another object is to obtain a refractory coating on ametal without deleterious contamination of the original metal surface byparticles of the blasting medium. Another object is to substitute a mildsurface-cleaning operation for a severe blasting operation and yetobtain superior adhesion Without metal distortion. Another object is toroughen the surface being coated by employ- 2 ing a sprayed metalcoating. Another'object is to interpose oxidation resistant metal layerbetween a slightly permeable refractory oxide coating and an oxidiz'ablebase metal. Another object is to provide a heat-resistingoxidizatio'n-r'esisting' metal layer between a base material and arefractory oxide flame-sprayed coating.

Other objects will be in part obvious or in part pointed outhereinafter.

For the formation 'of articles according to the invention, I procure ametal spray gun of the general type disclosed in patent to Erika Morf,No. 1,100,602 of June 16, 1914. Such metal spray guns are now well knownand are readily available on the market so need not further bedescribed. The metal in the form of a rod or wire is fused, atomized andsprayed by the gun and projected onto a surface the form of discretemolten particles which freeze in situ.

I further provide another spray gun, or under certain circumstances itmight be the same one. This may have the characteristics disclosed in myLetters Patent No. 2,707,691 of May 3, 1955. This gun is for the purposeof coating material with refractory oxide. In general a spray gun whichis suitable for fusing, atomizin'g and spraying refractory oxide can beused for fusing, atomizing and spraying metals so long as the metal isprovided in the form of wire or a rod of the proper diameter for the gunand the gun has adjustments for the feed and the flame so as to adapt itto the spraying of metal. In

other cases, I may use a gun for flame spraying the refractory oxidethat is adapted for the spraying 'of the oxide constituent in powderform. Also, a powder-gun may be used for the metal spraying. I

I provide an article or some material which is to be coated inaccordance with the invention. This may be any of those materialsindicated in the objects in solid phase provided it is reasonably rigid.This I call the base member: In many embodiments of the invention thebase member is a piece of metal, either a shaped metal part or a pieceof sheet metal. In other embodiments the base member may be a plastic,meaning a piece of organic material which can be molded, extruded orotherwise shaped, such as a piece of phenol-formaldehyde resin, o'fmetha'crylate polymer, of styrene or many other organic materials usedin the plastics industry. Hard rubber can be used for the base memberand also rigid article's made 'of rubber substitute material such asbu'tadiene styrene, butadiene acrylic nitrile and chlorinated butadiene.

EXAMPLE I I caused six pieces of stainless steel to be coated to producearticles according to my invention. The stainless steel was No. 321stainless steel (American Iron and Steel Institute). The pieces ofstainless steel were squares two inches by two inches and a sixteenth ofan inch thick. These constituted the base members. They were sandblastedwith Pangborn G-25 steel grit, at 40 pounds per square inch, until auniformly roughened surface was obtained. They were then spray coatedwith nickel using a Metco metallizing gun with one-eighth inch wirefeed. Following this, alumina was sprayed on with a gun of the typedescribed in US. Patent No. 2,707,691. The air pressure was to poundsper square inch. In each case the flame was produced by burningacetylene with oxygen and in each case a blast of air was used foratomizing and spraying. The control of the valves for feeding gases tothe spray gum is well understood by workers in this art and need not bedescribed in detail as is also the control of the feeding mechanism andfurthermore all of this is described in the aforesaid patents and in thecase of metal spraying in many other patents.

The first coating of nickel upon the stainless steel was fof the basemember. from discrete molten particles of metal frozen in situ on 3 .004to .008 inch thick. The superimposed coating of alumina, which is acoating of refractory oxide stable in air at room temperature and has amelting point of over 1000 C., was .010 to .020 inch thick. Actuallythis alumina coating was substantiallycompletely crystalline and itsmelting point as determined by recent evaluations is 2015 'C. C.

The coatings and the bases constituted integral pieces. The adhesivestrength between the coating of metal and thecoating of refractory oxide(alumina) was 'substantially equal to the cohesive strength of therefractory oxide coating. The individual particles of the coating ofmetal and the individual particles of the coating of refractory oxidewere self-bonded together so that each coating constituted arigidintegral structure independently The metal coating was made up the basemember. The alumina coating was made up from discrete molten particlesof oxide frozen in situ on the metal coating. Nickel has a melting pointof 1455 C. Both the nickel and the alumina, otherwise known as aluminumoxide, were substantially pure.

The adhesion between base metal and refractory oxide coating may oftenbe mechanical in nature. Under these conditions the degree of surfaceroughness of the metal becomes an important factor'toward good adhesion.Me-

chanical anchorage is aided by reentrant angles which are often present.

Under some circumstances chemical adhesion may be involved. Observationshave been made on a specimen with a nickel coating on stainless steel,which had been given a final coating of zirconia. It was subjected tocyclic heating and cooling and withstood the treatment very well. Darkareas that were thought to be nickel oxide were observed in microscopicexamination of a cross section, and this nickel oxide may havecontributed to the superior performance by a chemical or physicalmechanism. EXAMPLE H I provided more pieces of stainless steel insquares 'two inches by two inches and a sixteenth of an inch thick theother was zirconia.

4 The fourth and fifth lots were given a metal spray coating of nickeland the sixth and with alumina and some were coated with nickel-chromiumalloy prior to coating with zirconia. The nickel-chromium alloy that wasused was Nichrome, which is 60%-80% nickel, 11%-20% chromium and thebalance iron. Just where in this range the particular metal used was, Iam not sure, but all through this range the difference would bepractically immaterial. I believe the wire used for spraying the metalcoating was 60% Ni, 24% Fe and 16% Cr.

The following is a description of the samples, their preparation forcoating, the coating operation, the thickness of coatings, and the testprocedures:

Specimens.--Forty-two specimens of size 2" x 2" x 5 were sheared out ofa sheet of 321 stainless steel.

Preparation.All specimens were blasted with Pangborn G-25 steel grit at40 to pounds per square inch pressure. Grit impinged on the plates at anangle of about 90. Blasting was just sufficient to produce a uniformlyrough surface. This caused specimens to be slightly convex due tocompressive stress having developed in the surface because of theimpact.

' Coating 0perazi0n.Coating was carried out with the equipment describedin Example I. Specimens were separated into seven lots of six specimenseach. Three lots were coated with refractory metal oxide directly on theblasted stainless steel surface. The coating for two of these lots wasalumina (thus giving two identical lots, of which one can be considereda check test) and for seventh lots were given a metal spray coating ofNichrome. Then the fourth and sixth lots were coated with alumina andthe fifth and seventh lots were coated with zirconia.

Coating thickness-Oxide coatings were 0.015: 0.005 thick. Metalundercoatings were 0.006"i0.002 thick.

Test pr0cedure.--All specimens were then put through a test to determinethe relative ability of the coatings to withstand repeated heating andcooling. A laboratory electric furnace was heated to 1040 C. The sixtest specimens constituting a single lot were placed side by side,coatedside down, on a flat piece of stainless steel screen of about A"mesh. The screen with the speci-. mens on it was then placed on thebottom of the furnace, and the door was closed.

After 60 seconds the screen with the red hot specimens on it at atemperature of about 1000 C., were withdrawn from the furnace andsupported over a vertical stream of fan-driven room temperature airmoving at about 300 feet per minute. This brought the samples down toroom temperature in three or four minutes. They were then examined todetermine the condition of the coating, and the cycle was repeated.

Failure criteria.Lifting or flaking off of a small amount of coatingconstituted failure. The number of cycles to failure was recorded.

The results were as given in the following table.

Table I RESULTS OF CYCLIC HEATING AND COOLING TEST Lot Coating Max. Min.Avg. Type Failure No. Cycles Cycles Cycles 1;--. Alumina 6 1 3% Coatinglifted from base metal at corners. 2.--- Alumina, 4 1 2 Same as above.

Check Test. 3---- Zirconia 11 6 7% Edges failed by slight lifting ofcoating. 4--.- Nickel under 10 3 8 Alumina lifted Alumina. slightly fromnickel undercoat at edges. 5-.-- Nickel under Over 40. 40 40+ Slightcrumbling Zirconia. at edges, no

lifting. 6-- Nlchrome under Over 40 9 34+ Edge crumbling Alumina. withslight litting of alumina coating from Nichrome undercoat at corners. 7Nichronre under Over 40 40 40+ Slight crumbling ircoma. at some edges.

Another method of formation of the metal undercoating for articlesaccording to the invention utilizes electric arc sputtering of thecoating metal on to the base surface, in this case a metal or otherconductor of electricity. The coating metal, in the form of a rod,functions as one electrode; the base material as the other electrode. Agenerator, such as is used in arc welding, is used to develop sufiicientvoltage difference between the base material and the coating metal rodso that an arc is drawn between the two when they are broughtsufliciently close together. The are causes bits of the rod to be meltedand fused'onto the base material. The rod of metal to be used as coatingis held in a pistol type holder on which is mounted an air vibrator thatcauses the holder and rod to vibrate, depositing the metal coating indiscrete molten particles which freeze in situ. Then the oxide coatingis applied over-the metal coating as previously described. Coating withmetal by sputtering is known per se and has been described in patentsand technical literature.

EXAMPLE III Four stainless steel plates, supplied for test panels by aleading manufacturer of jet engines, were of size about 6" x 2%" x $1These were sandblasted with 6-25 crushed steel shot and thenspray=metallized with 5 mils of nickel followed by refractory oxidespray coating of 25 mils thickness by the process of US. Patent No.2,707,691. Two plates were thus coated with alumina and two withstabilized zirconia.

The heating tests were made under simulated engine conditions in thelaboratory of the jet engine manufacturer, who reported that the steelplates, m'etallized with nickel, and flame sprayed with alumina andzirconia coatings, showed marked improvement over all panels previouslysubmitted. The manufacturer also reported that the alumina panel becameloose near the ends, but failure was in the coating itself, and not atthe interface. The manufacturer further reported that the zirconia waseven more adherent; showing no indications of failure in one test, andonly slight shear failure (within the coating) near one corner of thepanel in another test.

Various examples of my invention have been produced experimentally whichwill have many practical uses in accordance with the objects andotherwise. Among them are the following:

In place of the alumina in all of the above examples could besubstituted zircon, zirconia, chromium oxide, wollastonite, spinel, etc.

EXAMPLE IV Other test samples which have been made experimentallyinclude employment of a base member of cemented tungsten carbide in onecase, and stainless steel in another. A rough layer of nickel wasdeposited employing the sputtering process previously described. Afterthis, an alumina coating 10 to 20 mils thick was sprayed over thenickel. There was excellent adhesion of the alumina coating. Othermetals and other hard carbides such as are used for tool bits, etc.,could have been used. However, for the sputtering process, the basemember must be electrically conducting.

EXAMPLE V Multiple coatings can be achieved. For example, black ironspecimens were used in one series of experiments. These were roughenedby grit-blasting at 40 pounds per square inch pressure and a nickelcoating about 6 mils thick was sprayed on using Ma nickel wire. Then amoderately soft alumina coating was sprayed on using a powder gun (modelA gun of Wall Colmono'y (30., Detroit), with alpha alumina monohydrateas feed. 'Following this, a coating of hard alumina was "sprayed onusing a /s" alumina rod as described in Example I. The article producedhad a hard alumina erosion resistant surface coating with a laminarmicrostruc'ture which adapted it to withstand heating and coolingstresses without flaking off, with yieldable alumina back-up layer andnickel anchoring layer. Other oxides and combinations of oxides, as wellas other metals, can be used. 7

Other combinations of multiple coatings and sandwich coatings may beemployed depending on the use conditions. For example, the metalundercoating may be sprayed on with a metallizing gun and then heated onthe surface to consolidate the particles and render the coating lesspermeable or substantially impermeable. Torching the surface is onewayto accomplish this. If the heated surface is not sufliciently rough toserve as good anchorage for the refractory oxide layer, then it may beroughened by sandblasting or by other methods such as further metalspray deposition.

Alumina over aluminum on steel;

Alumina over copper on steel; I Alumina over iron on steel, especiallystainless steel; Alumina over molybdenum on steel;

Alumina over cobalt on steel;

Alumina over Monel metal on steel;

Alumina over Inconel on steel.

6 EXAMPLE VI Two specimens of black iron were grit blasted at 40 poundsper square inch with steel grit to produce a roughened surface and thenspray-coated using the model A Wall Colmonoy gun feeding ti'n powder inone case and lead powder in another. They were then sprayco'ated withalumina by the process of Example I. A good adherent hard aluminacoating was obtained in both cases. Care had to be taken to avoiddeleterious melting of the tin undercoating, during the aluminaspraying, due to its low melting point of 232 C.

The gun of patent, under suitable conditions, is capable of sprayingrefractory oxides over stable metals including alloys with meltingpoints at least as high as 200 C. However, refractory metals withmelting points over 1000'? C. are particularly adapted forhigh-temperature refractory purpose use in conjunction with refractoryoxides of melting points over i000" C. Oxides and metals that arerefractory to chemical and erosive action can be useful for manypurposes at less-elevated temperatures, and even at room temperature orbelow.

A preferred metal undercoa'ting is in the range of 4 to 15 milsthickness but thinner and thicker coatings such as from 1 to 30 mils ormore are usable. Likewise, a usuallypre ferred refractory oxide coatingthickness is in the range from 5 to SO mils but thinner and thickercoatings such as from 2 to 200 mils or more may be desirable dependingon the use conditions. There is nothing critical about any of theseranges and the most practical thicknesses 'are chosen as the bestcommercial balance in each case between cost and performance under theuse conditions desired, such as degree of heat insulation, corrosionresistance, heat-shock resistance, erosion resistance, etc. of theproduct.

Rough surfaces on the metal coating are desirable as 'a foundation forthe refractory oxide coating. Reentrant angles in the surface hills andvalleys are helpful. The exact desired degree of roughness will dependon several factors such as the use conditions, the configur'a tion ofsurfaces coated, the sand-blasting medium and blasting techniques ifblasting is employed, the metallizing techniques if metallizing isemployed as the rougheni'ng agent to help to anchor the final refractoryoxide coating in place. Cost and use requirements have to be balancedcommercially. Concave surface configuration, especially insidecylindrical surfaces, heated in use on the inside such as combustionchambers and rocket nozzles are particularly satisfactory for givinggood results. Sandblasting with hard tough inorganic abrasives such asfused alumina or silicon carbide avoid surface embedding with particlesof metal grit that may occur when crushed steel shot is used.

Likewise the surface of the base member should be sufliciently clean andrough to give :good adhesion with the metal undercoating. My work,however, indicates in general that the surface roughness condition ofthe base member is of less importance as an anchoring factor for themetal coating, than is the surface condition of the metal coating as ananchoring factor for the refra'ctory oxide coating. Thus a lightlycleaned base member surface is often adequate for anchoring the metalundercoat to the base member, and the rough surface obtained directly onthe metal layer coating such as with a metallizing gun or with asputtering process, by depositing heat-plasticized metallic particles,is adequate for anchorage to the refractory oxide coating. Under theseconditions, one feat ure of the step of applying a metal layer coatingto a base member becomes a process of roughening the surface ofapplication for the refractory oxide coating to promote adhesion to thebase member. If the metal undercoating layer is deposited by proce ssesthat do not leave it with a sufficiently rough surface, then it can beroughened in other ways such as by sandblasting. Eleetroplating leaves asmooth surface.

7 Articles made in accordance with the invention are useful for all ofthe purposes described in the objects. Combustion chambers of reactionmotors and the nozzles of rocket motors are more resistant to flame andwill last longer when coated in accordance with this invention usingoxidation resistant metal undercoating, than when coated merely inaccordance with my prior patent which itself greatly advanced the art.The outstanding improvement in length of life under thermal shock madeby the combination coatings of the invention is hard to explain.

Any refractory oxide having a melting point of over 1000 C. and whichwill form a coating as described can be used in accordance with thisinvention. A long list of complex oxides which can be used is given atthe top of column in my aforesaid Patent No. 2,707,691 and in column 7of this patent is a general discussion of the oxides mentioning many ofthe better ones.

All of the metals which are stable in air and have a melting point ofover 200 C. can be used but for many practicable applications of theinvention an oxidation resistant metal will be preferred. 'For thepurposes of this invention an oxidation resistant metal is defined as ametalor an alloy which is at least asresistant to oxidation as isstainless steel at a temperature of 1000 C. in air. For purposes of thisinvention the term alloy is intended to include commercially pure metalsas well as higher alloyed compositions.

The elementary metals which as such are oxidation resistant and whichare components of many oxidation resistant alloys are, excluding suchnoble metals as platinum and gold which are most oxidation resistant buttoo expensive for most applications, nickel, cobalt and chromium.

In general, heat resistant oxidation resistant alloys can be classifiedinto groups based respectively on nickel, cobalt and iron, in which theclassification name corresponds to the ingredient that is present inhigher numerical amount than any other ingredient of the alloy. Althoughchromium is an important ingredient in many of these alloys, chromiumbase alloys are not usually important today.

Typical heat resistant alloys are given in the following table.

Table II TYPICAL HEAT RESISTING ALLOYS Percentage by Weight Ni Or 00 FeW Mo Ti Al Nb Nickel Base:

Nichrorne I l1 Nichrome V 20 Inconel.-- 15 M252 19 Cobalt Base:

Haynes Stellite No.31 25 55 1 8 Haynes Stellite 8-816 20 20 43 4 IronBase:

Timken l6-256 25 16 51 18-8 Stainless SteeL. 8 18 74 Kanthal A 23 2 69Smith No. 10 37% 55 the step of coating the metal coating withrefractory metal oxide involves fusing the metaloxide to form moltenmetaloxide and atomizing it and projecting it upon the surface of themetal coating. In the above, fusing is synonymous with melting.

When I say that the melting point of the metal is at least as high as200 C., I mean that 200 C. is the grinimum and this is substantially thesame as stating that the melting point of the metal is above 200 C.Similarly the melting point of the oxide must be at least 1000 C.meaning at least as high as 1000 C. and this is substantially the sameas stating that the melting pointv of the metal oxide should be over1000 C. Especially in the upper range a diiference of one degree is ofno consequence in temperature limits like these.

The atomizing of the metal in accordance with the preferred embodimentof this invention is achieved by the use of a blast of gas as describedin many prior patents, for example the patent to Morf referred to andother patents, such as the patent to Schoop, No. 1,128,058, referred toin my prior patent. As described in my prior patent referred to hereinthe molten metal oxide is atomized in like manner, namely by the use ofa blast of gas. Usually in both cases the blast of gas is largely airbut the prodnets of combustion of the gases such as acetylene and oxygenis part of said blast.

It will thus be seen that there has been provided by this inventionoxide coated metal coated articles in accordance with which the variousobjects hereinabove set forth together with many thoroughly practicaladvantages are successfully achieved. As many possible embodiments maybe made of the above invention and as many changes might be made in theembodiments above set forth, it is to be understood that all matterhereinbefore set forth is to be interpreted as illustrative and not in alimiting sense.

I claim:

1. Process for coating rigid materials to protect them from oxidationand for other purposes comprising fusing metal having a melting pointover 200 C. thus producing molten metal, atomizing said molten metal toproduce particles of molten metal, freezing the particles in situ uponthe rigid piece of material to form a metal coating thereon, thereafterfusing material consisting of refractory metal oxide which has a meltingpoint of over 1000 C. producing thereby molten metal oxide, atomizingthe molten metal oxide to form discrete molten particles thereof,coincidentally projecting said molten particles of metal oxide on to thesurface of said metal coating and freezing the molten particles of metaloxide in situ thereon to form a coating of said metal oxide having amelting point of over 1000 C. upon said metal coating.

2. Process according to claim 1 in which, after the particles of moltenmetal are frozen in situ upon the rigid piece of material to form ametal coating thereon, the metal coating is roughened to promoteadherence of the coating of metal oxide thereon.

3. Process according to claim 1 in which the molten metal is atomizedwith a blast of gas to produce the particles of molten metal.

4. Process according to claim 1 in which a second coating of metal oxidewhich is only oxide and of different characteristics from said coatingof metal oxide is superimposed upon the first coating of metal oxide bythe steps of fusing and atomizing the metal oxide for the secondcoating, projecting it upon the first coating and freezing it insituthereon.

5. Process according to claim 1 in which the coating of refractory metaloxide is produced from a sintered rod of said oxide.

n 6. Coating process for the protection of oxidizable rigid materialscomprising applying a coating of metal having a melting point over 200C. to a piece of said material, then fusing, atomizing and sprayingmaterial consisting of refractory metal oxide which has a melting pointof over 1000 C. on to said coating of metal.

7. Process according to claim 6 in which the surface of the metalcoating is roughened prior to the fusing, atomizing and spraying of themolten metal oxide.

8. Process according to claim 6 in which the coating of refractory metaloxide is produced from a sintered rod of said oxide.

9. Process for coating metals comprising providing a metal base memberto be coated, applying a coating of metal having a melting point over200 C. to said metal base member, then fusing a rod of materialconsisting of refractory metal oxide and atomizing and spraying saidfused material which has a melting point of over 1000 C. on to saidcoating of metal.

10. Process according to claim 9 in which the metal base member iscoated with metal by means of fusing, atomizing and spraying metalhaving a melting point over 200 C.

11. Process according to claim 9 in which said rod is formed of sinteredrefractory metal oxide material.

12. A process for coating rigid materials to protect them from oxidationand for other purposes comprising fusing a refractory metal having amelting point over 1000 C. thus producing molten metal, atomizing saidmolten metal, to produce particles of molten metal, freezing theparticles in situ upon the rigid piece of material to form a metalcoating thereon, thereafter fusing material consisting of refractorymetal oxide which has a melting point of over 1000 C. producing therebymolten metal oxide, atomizing the molten metal oxide to form discretemolten particles thereof, coincidentally projecting said moltenparticles of metal oxide on to the surface of said metal coating andfreezing the molten particles of metal oxide in situ thereon to form acoating of said metal oxide having a melting point of over 1000 C. uponsaid metal coating.

13. A process for coating rigid materials to protect them from oxidationfor other purposes comprising fusing a refractory metal having a meltingpoint over 1000 C.

thus producing molten metal, atomizing said molten metal, to produceparticles of molten metal, freezing the particles in situ upon the rigidpiece of material to form a metal coating thereon, thereafterprogressively feeding and fusing a rod of material consisting of asintered rod of refractory metal oxide which has a melting point of over1000 C. producing thereby molten metal oxide, atomizing the molten metaloxide to form discrete molten particles thereof, coincidentallyprojecting said molten particles of metal oxide on to the surface ofsaid metal coating and freezing the molten particles of metal oxide insitu thereon to form a coating of said metal oxide having a meltingpoint of over 1000 C. upon said metal coating.

14. A coating process for the protection of oxidizable rigid materialscomprising applying a coating of refractory metal having a melting pointover 1000 C. to a piece of said material, then spraying fused atomizedmaterial, consisting of refractory metal oxide which has a melting pointof over 1000' C. on to said coating of metal.

15. A coating process for the protection of oxidizable rigid materialscomprising applying a coating of refractory metal having a melting pointover 1000 C. to a piece of said material, then fusing, atomizing, andspraying material consisting of refractory metal oxide which has amelting point of over 1000 C. on to said coating of metal.

16. Process according to claim 15 in which the coating of refractorymetal oxide is produced from a sintered rod of said oxide.

References Cited in the file of this patent UNITED STATES PATENTS2,707,691 Wheildon May 3, 1955 2,730,458 Schulze Jan. 10, 1956 2,839,292Bellamy June 17, 1958 2,930,106 Wrotnowski Mar. 29, 1960

1. PROCESS FOR COATING RIGID MATERIALS TO PROTECT THEM FROM OXIDATION AND FOR OTHER PURPOSES COMPRISING FUSING METAL HAVING A MELTING POINT OVER 200*C. THUS PRODUCING MOLTEN METAL, ATOMIZING SAID MOLTEN METAL TO PRODUCE PARTICLES OF MOLTEN METAL, FREEZING THE PARTICLES IN SITU UPON THE RIGID PIECE OF MATERIAL TO FORM A METAL COATING THEREON, THEREAFTER FUSING MATERIAL CONSISTING OF REFRACTORY METAL OXIDE WHICH HAS A MELTING POINT OF OVER 1000* C. PRODUCING THEREBY MOLTEN METAL OXIDE, ATOMIZING THE MOLTEN METAL OXIDE TO FORM DISCRETE MOLTEN PARTICLES THEREOF, COINCIDENTALLY PROJECTING SAID MOLTEN PARTICLES OF METAL OXIDE ON TO THE SURFACE OF SAID METAL COATING AND FREEZING THE MOLTEN PARTICLES OF METAL OXIDE IN SITU THEREON TO FORM A COATING OF SAID METAL OXIDE HAVING A MELTING POINT OF OVER 1000*C. UPON SAID METAL COATING. 